Sequence of constructor calls in multiple inheritance - c++

Question

I have tried to find a lot that what if only one class is made virtual in multiple inheritance?
The behaviour of constructor call is not clear to me in this case.
Let say for example code-
#include<iostream>
using namespace std;
class grand{
public:
grand(){cout<<"grandfather"<<endl;}
};
class parent1:virtual public grand{ //virtual used only here
public:
parent1(){cout<<"parent1 "<<endl;}
};
class parent2: public grand{
public:
parent2(){cout<<"parent2"<<endl;}
};
class child:public parent1,public parent2{
public:
child(){cout<<"child"<<endl;}
};
int main() {
child s;
return 0;
}
The output of this code comes as
grandfather
parent1
grandfather
parent2
child
but in above code if we change this
class parent1:virtual public grand{
public:
parent1(){cout<<"parent1 "<<endl;}
};
class parent2: public grand{
public:
parent2(){cout<<"parent2"<<endl;}
};
to this
class parent1:public grand{ //virtual removed from here
public:
parent1(){cout<<"parent1 "<<endl;}
};
class parent2:virtual public grand{ //virtual is added here
public:
parent2(){cout<<"parent2"<<endl;}
};
output is shown as
grandfather
grandfather //why parent1 constructor is not called here?
parent1
parent2
child
My concern is why parent1 constructor is not called after grandfather?

Answer 1

The standard says [C++11 section 12.6.2/10] that :
In a non-delegating constructor, initialization proceeds in the
following order:
— First, and only for the constructor of the most derived class,
virtual base classes are initialized in the order they appear on a
depth-first left-to-right traversal of the directed acyclic graph of
base classes, where “left-to-right” is the order of appearance of the
base classes in the derived class base-specifier-list.
— Then, direct base classes are initialized in declaration order as
they appear in the base-specifier-list (regardless of the order of the
mem-initializers).
— Then, non-static data members are initialized in the order they were
declared in the class definition (again regardless of the order of the
mem-initializers).
— Finally, the compound-statement of the constructor body is executed.
So your virtual base classes are always built first... This is really important in the case of virtual base class sharing.